Interpretive Summary: Storing rain in the soil during fallow is crucial for good dry land wheat and grain sorghum crops on the U.S. Southern High Plains. No-tillage (NT) crop residues usually increase rain infiltration. More rain has been lost as runoff from a Pullman clay loam using NT than stubble-mulch (SM) tillage at the USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas. Intensive crop rotations, like continuous wheat (CW), increase the efficiency of fallow (FE) to store rain over the wheat-sorghum-fallow (WSF) rotation. To learn how tillage, residue, and crop rotation affect FE, our experiment quantified infiltration of rain into NT or SM tilled long-term CW and WSF sites that were bare or straw covered. Infiltration increased with straw cover for any combination of tillage or crop rotation. Infiltration into bare sites did not vary with tillage. The more intensive CW rotation improved aggregates, increased infiltration, and reduced soil loss over the WSF rotation. Our results suggest more intensive rotations that keep residue can improve FE by increasing infiltration.

Technical Abstract:
Increased precipitation storage as soil water is crucial to dryland production of wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] on the semiarid Southern Great Plains. At the USDA-ARS, Conservation and Production Research Laboratory, Bushland, TX (35 deg 11' N, 102 deg 5' W), surface runoff from a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) is typically less under dryland conditions with stubble-mulch (SM) tillage than for no-tillage (NT) of either continuous wheat (CW) or wheat grown in rotation with grain sorghum and an intervening fallow (WSF). Our objective was to quantify the effects of NT or SM tillage with bare or retained residue on infiltration of simulated rain, sediment transport, and related soil properties for long-term CW and WSF rotation plots. Compared with bare soil, the retained wheat residue cover increased mean 60 minute cumulative infiltration across all tillage and rotation combinations by more than 25 mm and decreased soil loss. Cumulative rain infiltration and total soil loss did not vary significantly (p less than 0.05) with tillage, but the infiltration rate at 60 minutes was decreased by NT. The CW rotation typically increased infiltration regardless of residue cover or tillage compared with the WSF rotation, which we attributed to greater aggregate stability. The greater aggregate stability for CW may have decreased soil loss compared with WSF, which was greatest for bare SM tilled sites. We conclude that residue cover significantly increases rain infiltration over bare soil conditions independent of any tillage or rotation treatment effects. Nevertheless, we observed a lower mean infiltration rate at 60 minutes under no-tillage than where stubble-mulch tillage disturbed the soil.